After removing R39/TR3/C46, leakage amount was even higher than you observed, but only between drain and gate.

I remedied the PCB leakage via carefully digging “trenches” on either side of board using an exacto knife until measuring no connection. This seemed safer than drilling through, and was effective. As the board is double-sided as opposed to multi-layer, there is little chance of connection _within_ the substrate.

Also I upgraded the R39/R38 pair to from 1W to 2W metal film resistors to get a little extra safety margin.

i am confused r33 is this the real tiny resistor labeled r33 in little white ink or the big white box that says 7w33ohmj i saw a video of a guy biasing the ht 20 and it looked like he clipped his multimeter clips to the bottom of that box first but i looked again and he is clipping it to the white box at the bottom is this what you are talking about

I have a problem, I made the repair you say but I get that voltage at all points of the valve 220v only appear approximately ‘ve measured SP5 and I get at most 350V and 220V SP4 . I have problems with the transformer ????

Anytime! Some other issue can be which is the two capacitors 1uf 450V c45, c46 heating up then causing the MOSFETs tr2&tr3 to distort the signal. Better replacing those with non electrolytic capacitors and new mosfets in that case.

I had a Blackstar HT5-5TH with no sound. After much searching, I found that the op amp on the back board, next to the Send/Return jacks, was bad. Signal in from the return jack would not pass through it. I should have known earlier when I found signal coming out the Send jack, but inserting signal into the Return jack did nothing. Thanks for lots of ideas and info on what goes wrong with these amps. I think they are overly-complicated.

Thanks for sharing this info. I fixed mine yesterday, purchased as broken. R39 was burnt. Drain source resistance at position TR3 in my amp was even below 5 kΩ!!! and infinite after drilling a 1 mm hole. Now it is fixed